Actuating mechanism for deployment and retraction of an aircraft flight control surface may have a no-back device incorporated therein to prevent any movement of the flight control surface other than obtained by operation of a prime mover for the actuating mechanism. A typical no-back device has releasable brake means associated with an output shaft and a drive train between an input shaft associated with the prime mover and the output shaft. This drive train has a ball and ramp structure operable in response to torque flow from the input shaft in either direction of rotation thereof to release the brake means and transmit torque to the output shaft. The no-back device assures that a flight control surface will remain in whatever position is established by operation of the prime mover. An example of such a no-back device is disclosed in Twickler Pat. No. 4,176,733, owned by the assignee of this application.
If power is lost to the prime mover during deployment of an aircraft flight control surface with the actuating mechanism having the no-back device described in the preceding paragraph, the aircraft flight control surface will remain in a position to which it has been moved by the prime mover prior to loss of power. The unidirectional no-back device disclosed herein precludes aerodynamic loading on the flight control surface from further deploying the flight control surface while enabling the flight control surface to retract to a null position under aerodynamic loading in a direction to exert the necessary force thereon and cause backdriving of the prime mover.